Method and apparatus for a porous metal electrospray emitter

Abstract

An ionic liquid ion source can include a microfabricated body including a base and a tip. The microfabricated body can be formed of a porous metal compatible (e.g., does not react or result in electrochemical decaying or corrosion) with an ionic liquid or a room-temperature molten salt. The microfabricated body can have a pore size gradient that decreases from the base of the body to the tip of the body, so that the ionic liquid can be transported through capillarity from the base to the tip.

1. An ionic liquid ion source comprising:
 a microfabricated body comprising a base and a tip and formed of a porous metal compatible with at least one of an ionic liquid, or room-temperature molten salt; and 
 wherein the microfabricated body has a pore size gradient that decreases from the base of the body to the tip of the body, such that the ionic liquid is capable of being transported through capillarity from the base to the tip. 
 
     
     
       2. The ion source of  claim 1  wherein the ionic liquid is capable of being continuously transported through capillarity from the base to the tip. 
     
     
       3. The ion source of  claim 1  wherein the body is a cylindrical needle. 
     
     
       4. The ion source of  claim 1  wherein the body is a flat ribbon-like needle. 
     
     
       5. The ion source of  claim 1  wherein the tip is formed by electrochemical etching. 
     
     
       6. The ion source of  claim 1  wherein the porous metal is at least one of tungsten, nickel, magnesium, molybdenum or titanium. 
     
     
       7. The ion source of  claim 1  wherein a radius of curvature of the tip is approximately 1-20 μm. 
     
     
       8. An ionic liquid ion source comprising:
 a plurality of emitters microfabricated from a porous metal compatible with at least one of an ionic liquid, or room-temperature molten salt; and 
 wherein each emitter has a pore size gradient that decreases from the base of the emitter to the tip of the emitter, such that the ionic liquid is capable of being transported through capillarity from the base to the tip of each emitter. 
 
     
     
       9. The ion source of clam  8  wherein the ionic liquid is capable of being continuously transported through capillarity from the base to the tip of each emitter. 
     
     
       10. The ion source of  claim 8  wherein the porous metal is at least one of tungsten, nickel, magnesium, molybdenum or titanium. 
     
     
       11. The ion source of  claim 8  wherein the emitters are formed by electrochemical etching. 
     
     
       12. The ion source of  claim 8  wherein a spacing between the emitters is less than approximately 1 mm. 
     
     
       13. A system for producing ions comprising:
 a source of at least one of ionic liquid or room-temperature molten salt; 
 an array of emitters microfabricated from a porous metal compatible with the at least one of ionic liquid or room-temperature molten salt, wherein each emitter has a pore size gradient that decreases from the base of the emitter to the tip of the emitter such that the ionic liquid is capable of being transported through capillarity from the base to the tip of each emitter; 
 an electrode positioned downstream relative to the array of emitters; and 
 a power source for providing a voltage to the array of emitters with respect to the electrode. 
 
     
     
       14. The system of  claim 13  wherein the ionic liquid is capable of being continuously transported through capillarity from the base to the tip of each emitter. 
     
     
       15. A method for manufacturing an array of electrospray emitters comprising:
 applying polyimide to a first side of a sample comprising a porous metal compatible with an ionic liquid; 
 applying photoresist to the first side of the sample; 
 applying a transparency mask to the first side of the sample and exposing the sample to UV light to form an emitter geometry pattern; 
 removing the photoresist from the sample; 
 curing the sample to harden the polyimide; 
 electrochemically etching the sample to form an emitter geometry; 
 removing the polyimide resulting in an array of electrospray emitters; and 
 processing a tip of each emitter to vary a pore size between each tip and each base of each emitter in the array. 
 
     
     
       16. The method of  claim 15  wherein the step of processing comprises applying a layer of a compatible metal to a surface of each emitter at the tip of each emitter. 
     
     
       17. The method of  claim 16  wherein the step of processing comprises applying a layer of zinc to a surface of a tip of a porous tungsten emitter. 
     
     
       18. The method of  claim 15  wherein the step of processing comprises attaching carbon nanotubes to a surface of each emitter at the tip of each emitter. 
     
     
       19. The method of  claim 15  further comprising filling the porous metal with photoresist and exposing the porous metal with a UV light to block pores of the porous metal to form the sample. 
     
     
       20. The method of  claim 15  further comprising blocking the porous metal surface by the uniform deposition of mono-layers of a compatible metal using Chemical Vapor Deposition (CVD). 
     
     
       21. The method of  claim 15  wherein the step of applying polyimide to the first side of the sample further comprises prebaking the sample. 
     
     
       22. The method of  claim 15  further comprising the step of developing the sample to transfer the emitter geometry pattern by removing positive photoresist and etching the polyimide. 
     
     
       23. The method of  claim 15  wherein the step of electrochemically etching the sample comprises removing excess porous metal to form the emitter geometry. 
     
     
       24. The method of  claim 15  wherein the step of electrochemically etching the sample comprises etching the sample to form a conical emitter geometry. 
     
     
       25. The method of  claim 15  wherein the porous metal is at least one of tungsten, magnesium, molybdenum, titanium or nickel. 
     
     
       26. A method for manufacturing an ion emitter comprising:
 forming a body from a porous metal compatible with at least one of an ionic liquid or room temperature molten salt, the body having a pore size gradient that decreases from a first end of the body to a second end of the body; and 
 microfabricating the body to form a base relative to the first end of the body and a tip relative to the second end of the body, wherein the ionic liquid is capable of being transported through capillarity from the base to the tip. 
 
     
     
       27. The method of  claim 26  wherein the ionic liquid is capable of being continuously transported through capillarity from the base to the tip. 
     
     
       28. The method of  claim 26  wherein microfabricating the body comprises shaping the body into a flat ribbon-like needle. 
     
     
       29. A method for manufacturing an ion source comprising:
 forming an emitter geometry pattern on a unitary substrate comprising a porous metal compatible with at least one of an ionic liquid, or room-temperature molten salt; 
 electrochemically etching the unitary substrate to form a plurality of emitters, wherein each emitter comprises a base at the first end of the substrate and a tip at the second end of the substrate; and 
 processing the tip of each emitter to form a pore size gradient that varies from the base to the tip. 
 
     
     
       30. The method of  claim 29  wherein the ionic liquid is capable of being continuously transported through capillarity from the base to the tip of each emitter. 
     
     
       31. The method of  claim 29  wherein the step of processing comprises applying a layer of a compatible metal to a surface of each emitter at the tip of each emitter. 
     
     
       32. The method of  claim 31  wherein the step of processing comprises applying a layer of zinc to a surface of a tip of a porous tungsten emitter. 
     
     
       33. The method of  claim 29  wherein the step of processing comprises attaching carbon nanotubes at a surface of each emitter at the tip of each emitter.